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Abstract
Summary
The present study was performed into two experiments to investigate the effect of different approaches of feed restriction and the implication of realimentation in alternative weeks on chick performance, carcass traits and meat quality. The restriction approaches involved restriction of nutrients, protein and energy; feed intake; and the most valuable and expensive fish meal.
A total number of 330 one day-old broiler chicks of the Hubbard breed, were randomly distributed into eleven groups of 30 chicks each and allotted into two separate experiments of 6 and 5 groups respectively.
In experiment I, birds in the first group which was considered as a control were fed ad-libitum on a broiler grower diet (one diet–system) containing 20 % CP and 3200 kcal/kg ME. The diet was offered allover the experimental period from hatch to 7 weeks old. Chicks of the other five groups were offered the same diet in the starting stage (0-3 weeks). In group 2 and 3 restriction was tried on the CP dietary level, keeping the C/P ratio as that of the control. The CP% was reduced by 5% in group 2 to reach 19 (and ME 3050 Kcal/Kg diet) and by 10 % in group 3 to reach 18 % (and ME 2900 Kcal/kg diet). In the last three groups 4, 5& 6 the reduction was not experimented on the nutrient density but on feed intake, restricting the intake to 80, 70 & 60% of that consumed by the control group, in a respective order. As a trial to overcome the negativity and to get advantage of the ”compensatory growth” phenomenon the restriction weeks were interrupted by weeks of the ad-libitum feeding the control diet, on an alternative basis. So in the 4th & 6th weeks was the restriction and in the 5th &7th was realimintation.
In experiment II, the control diets, starter, grower and finisher having the 4 % FM level were used in group 1 while in group 2 & 3; the FM was restricted on a stage-basis (trial I). A corn/soya diets were fed in the finishing stage in group 2 and in the growing and finishing in group 3. The restriction followed in group 4 & 5 (trial II) was on the FM percentage where 3 % instead of 4 % was used allover the 7 weeks in group 4 and 2 % in group 5.
Each experiment was extended for 7 weeks duration in three feeding phases, starting through the first three weeks, growing from3-5 weeks and finishing from 5-7 weeks of age.
The following results were obtained :
Experiment I (restriction of energy, protein & feed intake)
1- In the starting phase (0-3 weeks), there were no significant difference in the live body weight in all treated groups and control.
2- Live weight gains of birds fed on energy-protein restricted diets were reduced by 22 % in the second and 32.5 % in the third group at 42 days of age compared to control one. However feeding broilers on energy-protein restricted diets in the second and third groups resulted in increasing of weight gain by 7.3 and 3.8% after energy and protein realimentation at 35 d of age.
3- Feed to gain ratios during the finishing period at 42 and 49 d were numerically increased in broilers fed restricted diets compared to those fed satisfactory diet (control).
4- The weekly body weight gain and relative growth rate of birds submitted to food restriction at 28 and 42 d of age was significantly (P<0.05) lower when compared to the birds fed ad-libitum. The retardation of growth was more pronounced for the 70 & 60 %-restricted birds ( 182 and 138g Vs 358 g for control) in the first stage and (132 &142 g vs 246 g for control) in the second stage of restriction.
5- Concerning the weight gain and relative growth rate during the first realimentation period (28 – 35 d), there were significant (P<0.05) differences between the different experimental groups and control. Birds of the 80% restricted group had highest gains followed by 70 and 60% treatments, where the weight gain reached 135.4, 129.4 and 105.2 % of that recorded in the control. In the second realimentation period (42 – 49 d), the weight gain was slightly increased in fourth group (70% restricted birds), while nearly similar to control in the other two restricted groups.
6- No significant differences among energy and protein restricted groups and control in carcass dressing value and weights of internal organs and, there was less abdominal fat as a percentage of live body weight at 49 d of age.
7- Data of slaughter studies showed that no differences in the percentages of internal organs in 80, 70 and 60 % restricted groups and control.
8- Restriction of energy and protein or feed intake had no effect on chemical composition of carcass and meat quality tests as well as total serum protein, albumin and globulin.
Experiment II :
1- The average values of body weight and the weight gains between fourth and fifth experimental groups were nearly similar with no statistical significance at the end of starting phase.
2- Live body weight of chicks at growing phase was significantly reduced in the third, fourth and the fifth groups where the weights reached 95, 92, and 84 of the control group respectively. The highest feed conversion index was achieved by chickens in the last group (1.93).
3- In the finishing period (5-7 weeks), birds in the third and fifth groups, had the significantly lowest body weight, which reach about 96 & 94 % of that control group. Live weight gain in the fourth and fifth groups which fed on low levels of fish meal did not show any negative effect but on the contrary a positive one to the degree the gain reached 116.7 and 129.8% of that recorded in the control.
4- The total body weight gains in the seven weeks of feeding in the second and fourth groups were not significantly different from that of the control, while the third and fifth treated groups scored the lowest gain (1889.8 & 1803.6g vs. 1974.4g).
5- Dressed carcass as a percentage of body weight were maximum in broilers offered 4 % FM diet through three stages, followed by second and third groups .The lowest dressed carcass values were scored in the fourth and fifth groups. The abdominal fat percentage at the end of the experimental period was maximum in the control group (1.63 %), while it was minimum in groups offered diets had low levels of fish meal.
6- Stage feeding programs of fish meal had no effect on dry matter, crude protein and ash content of carcass meat. However the highest value of ether extract was recorded with the control group and the lowest with group fed on 2% fish meal diet.
7- Total protein, albumin, globulin and meat quality parameters of birds in all experimental groups and control were not affected by stage feeding programs and varying levels of fish meal.